Lieutenant William Thomas Barnes DFC (10 March 1892 – 28 November 1920) was an English World War I flying ace. He served as an observer/gunner in Bristol F.2 Fighters, gaining, in conjunction with his pilots, nine confirmed aerial victories (6 destroyed, 3 'out of control') over German Fokker D.VII fighter planes. Post-war he served in the Royal Irish Constabulary and was killed in the Kilmichael ambush on 28 November 1920.